Heretofore, as an etching liquid for a Ti-based metal film such as Ti film and TiW alloy film, for example, hydrogen peroxide etching liquid, acidic etching liquid such as, for example, hydrofluoric acid—hydrogen peroxide mixed liquid, phosphoric acid—hydrogen peroxide mixed liquid, are known.
However, the hydrogen peroxide solution not only has a problem that when a metal such as, for example, copper, silver, gold is contained, decomposition of hydrogen peroxide is promoted and lifetime of the etching liquid is shortened, but also has such problems that it is difficult to control a concentration of hydrogen peroxide in the etching liquid and that etching rate is slow, and the like.
In addition, for example, the fluorine—hydrogen peroxide mixed liquid has such problems that, for example, etching rate is slow and that corrosion of underlying metal or metal on a substrate is significant, and the like, and the phosphoric acid—hydrogen peroxide mixed liquid has such problems, for example, that etching residue is generated and that corrosion of underlying metal or metal on a substrate is significant, and the like.
Under such circumstance, as an etching method for a Ti-based metal film such as Ti film, TiW alloy film without generating etching residue, an etching method for a Ti-based film on a semiconductor substrate using a solution containing hydrogen peroxide and a chelating agent has been proposed (see, JP-A-2002-155382).
However, depending on a kind of underlying metal or metal on a semiconductor substrate, such problems occur that etching selectivity is poor because, for example, corrosion of other metals occurs, and that lifetime of the etching liquid becomes shortened and etching rate becomes slow because, for example, decomposition of hydrogen peroxide is promoted, and the like.
In addition, in order to carry out etching for Ti or TiW alloy without discoloration of solder, for example, an etching liquid containing hydrogen peroxide, a phosphonic-acid-based compound, and the like has been disclosed (see, JP-A-2003-328159). However, as a phosphonic-acid-based compound, no compound other than nitrogen-containing phosphonic acid has been disclosed, and since such phosphonic-acid-based compound has such a problem that there is fear of stability when added to the solution containing hydrogen peroxide, for example, because the solution thereof is strongly colored and too many metal impurities are contained as an etching agent for a semiconductor substrate.
Under such circumstance, in processing of a semiconductor substrate provided with Cu wiring and a semiconductor substrate useful for forming lead (Pb)-free solder bump, developments of an etching method improving an etching selectivity of a Ti-based metal film and an etching liquid to be used for selective etching of a Ti-based metal film have been desired.
On the other hand, heretofore, since a coating used a metal having lower ionization tendency such as gold, silver has not only superior physical properties such as good electric conductivity, superior thermocompression bonding ability but also superior chemical properties such as oxidation resistance, chemical resistance, the coating has been suitably used for forming bump, wiring, and the like on a semiconductor substrate (see, JP-A-2007-100130, etc.).
In addition, on the other hand, for etching the tungsten (W) and/or titanium-tungsten (TiW) alloy in the presence of such metal having good electric conductivity, for example, an etching liquid characterized by containing at least an aqueous hydrogen peroxide solution and an alkali component and having pH of 7 or less, and the like have been known (see, JP-A-2004-31791, etc.). However, recently, since precision in wiring, and the like is desired, there is a problem that such etching liquid is not sufficient to inhibit side-etching of W, TiW alloy, and the like.